Phase Differential - GE MOTOR MANAGEMENT RELAY 469 Instruction Manual

4.7 S6 CURRENT ELEMENTS
S PHASE DIFFERENTIAL
S [ENTER] for more
4
These setpoints program the differential element when the differential feature is in use. This feature consists of
three instantaneous overcurrent elements for phase differential protection. Differential protection may be con-
sidered first line protection for phase to phase or phase to ground faults. In the event of such a fault, differential
protection may limit the damage that may occur.
Care must be taken when enabling this feature. If the interrupting device (contactor or circuit
breaker) is not rated to break potential faults, the feature should be disabled. Alternately, the
feature may be assigned to an auxiliary relay and connected such that it trips an upstream
NOTE
device that is capable of breaking the fault current. A low level differential fault can develop
into a short circuit in an instant.
A trip occurs once the magnitude of either I
Pickup Level × Differential CT Primary for a period of time specified by the delay. Separate pickup levels and
delays are provided for motor starting and running conditions.
The Differential trip element is programmable as a fraction of the rated CT. The level may be set more sensitive
if the Differential CTs are connected in a flux balancing configuration (3 CTs). If 6 CTs are used in a summing
configuration, the values from the two CTs on each phase during motor starting may not be equal since the CTs
are not perfectly identical (asymmetrical currents may cause the CTs on each phase to have different outputs).
To prevent nuisance tripping in this configuration, the STARTING DIFF. TRIP PICKUP level may have to be set less
sensitive, or the STARTING DIFF. TRIP DELAY may have to be extended to ride through the problem period during
start. The running differential delay can then be fine tuned to an application such that it responds very fast to
sensitive (low) differential current levels.
4-52
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PHASE DIFFERENTIAL

ENTER
TRIP: Off
ESCAPE
ASSIGN TRIP RELAYS:
ESCAPE
Trip
MESSAGE
STARTING DIFF.
ESCAPE
TRIP PICKUP: 0.10 x CT
MESSAGE
STARTING DIFF.
ESCAPE
TRIP DELAY: 0 ms
MESSAGE
RUNNING DIFF.
ESCAPE
TRIP PICKUP: 0.10 x CT
MESSAGE
RUNNING DIFF.
ESCAPE
TRIP DELAY: 0 ms
MESSAGE
- I
aIN aOUT
469 Motor Management Relay
4 SETPOINT PROGRAMMING
Range: Off, Latched, Unlatched
Range: Trip, Trip & Auxiliary2, Trip & Aux2 & Aux3, Auxiliary2,
Aux2 & Aux3, Auxiliary3
Range: 0.05 to 1.00 x CT, step: 0.01
Range: 0 to 1000 ms, step 1
Range: 0.05 to 1.00 x CT, step: 0.01
Range: 0 to 1000 ms, step 1
, I - I , or I - I (phase differential) exceeds the
bIN bOUT cIN cOUT
4.7.7 PHASE DIFFERENTIAL
GE Power Management